This invention relates in general to a method for making a magnetic head assembly. More particularly, this invention relates to an improved method for making a multi-head magnetic head assembly for use in high density magnetic storage devices.
Magnetic head assemblies used in magnetic tape recorders and magnetic disc drives must meet more demanding design specifications necessitated by higher density recording formats. Thus, in a high density magnetic tape recorder, the tape bearing surfaces (such as magnetic heads and non-magnetic faceplate surfaces) must be durable in order to provide long head life despite high pressure contact over the head gap area with highly abrasive magnetic tape media (such as chromium dioxide tape). The faceplate and heads should have compatible wear properties to prevent head undercut and separation loss. Moreover, the magnetic head assembly must have mechanical stability and be able to withstand environmental changes (temperature, humidity, shock and vibration) without performance degradation. The magnetic head core structure must be shielded to minimize crosstalk between heads in adjacent tracks and heads in the same track. The magnetic head assembly should also have a cost effective design in order to be competitive in a highly cost sensitive market.
Numerous proposals have been made to utilize both magnetic and non-magnetic ferrite in magnetic head assembly design. High density ferrites are generally mechanically stable and highly resistant to abrasion and provide good signal recording and reproduction characteristics. Typically, a multi-channel magnetic head assembly has been formed from a large number of individual elements. A typical head assembly, which is made of two half brackets or two half sheils screwed and/or epoxied together, would include individual ferrite or metal cores wound with the necessary turns of electrical conductor. The cores are loaded into half brackets, cemented in place and connected to electrical terminal boards or electrical connector plates inserted into the bottom of the half brackets. Tip plates which form the front surface of the magnetic head assembly are slotted to accommodate individual intertrack magnetic shields. The tip plates are are grooved to receive magnetic head tip pieces which are especially hard and durable. The tip plates are then attached to the core loaded half brackets to provide intimate contact between the tip pieces and the ferrite cores. The magnetic gap of each head is formed by vacuum deposition of silicon monoxide and the two half brackets bonded together. The front surface contacting the tape is then contoured (see for example, the Bell & Howell publication entitled "MAGNETIC TAPE RECORDING TECHNICAL FUNDAMENTALS", 4th printing revised, 1984, pp. 23 et. seq.; "THE COMPLETE HANDBOOK OF MAGNETIC RECORDING", by Jorgensen, 1980 ed., pub. by TAB Books, Inc., Blue Ridge Summit, PA pp. 158 et seq.; and U.S. Pat. No. 3,400,386, entitled "Multichannel Magnetic Head Assembly", issued Sept. 3, 1968, by R. C. Sinott). Such magnetic head assemblies are disadvantageous because of the difficulty and expense in producing them. Moreover a large number of assemblies must be discarded as unusable due to incorrect component positioning.
Multichannel magnetic head assemblies have also been proposed in which a plurality of magnetic ferrite heads are bonded to a split non-magnetic ferrite faceplate. Individual magnetic shields are then secured between adjacent heads to minimize crosstalk and the resultant structure mounted in an aluminum shell (see for example, U.S. Pat. No. 3,668,775, issued June 13, 1972, entitled "Method for Manufacturing Magnetic Heads", by Martai et al; and U.S. Pat. No. 3,789,505, issued Feb. 5, 1974, entitled "Method Of Making a Multi-Core Magnetic Head With A Non-Magnetic Holder", by R. L. Hunt). Such magnetic head assemblies are disadvantageous in the use of individual magnetic shields between adjacent heads and in the use of different ferrite materials in the faceplate structure which may produce mechanical instabilities.
Magnetic head assemblies are also known in which magnetic ferrite cores are mounted in non-magnetic ferrite holders and individual magnetic ferrite shields are inserted between adjacent magnetic heads (see for example, U.S. Pat. No. 3,909,932, issued Oct. 7, 1975, entitled "Method of Manufacturing A Multi-Track Magnetic Head", by W. L. Kroon; U.S. Pat. No. 3,842,494, issued Oct. 22, 1974, entitled "Multi-Channel Magnetic Ferrite Head And A Method For Making The Same", by H. Shiba et al; and U.S. Pat. No. 3,761,641 issued Sept. 25, 1973, entitled "Magnetic Head With Demountable Face Part Assembly", by T. A. Milnarick). Each of the magnetic head assemblies disclosed in these patents is disadvantageous because of the large number of parts required to form the magnetic head assembly and because of the difficulty in properly aligning the magnetic head gaps across the width of the assembly. Such magnetic head assemblies are complex and expensive to produce.
In order to reduce the number of individual parts used in a multi-head magnetic head assembly and in order to effect exact alignment of gaps across the width of the head assembly, it has been proposed to form several aligned heads from blocks of magnetic ferrite material which are ground down to form individual magnetic head core elements. This structure is then lapped, gapped and bonded to form a multi-head magnetic assembly. The individual heads may be commonly joined together by a portion of a magnetic ferrite block which has not been removed. Such an assembly is disclosed in U.S. Pat. No. 3,544,982, issued Dec. 1, 1970, entitled "Multi-Head Magnetic Assembly", by J. J. Hanak in which the back portion of the magnetic heads is commonly joined by magnetic ferrite which is integral with the individual head cores. U.S. Pat. No. 3,543,396, issued Dec. 1, 1970 entitled "Method Of Multi-Track, Two-Gap, Ferrite Magnetic Heads Design Especially For Digital Recording", by Z. Illg et al., discloses a magnetic head assembly in which three blocks of magnetic ferrite material are lapped, gapped and bonded together to form a unitary structure. This structure is ground down to provide a multi-track magnetic head assembly in which each track has a pair of heads. In the embodiments shown in FIGS. 6 and 7 of the latter patent, a centrally disposed solid magnetic ferrite piece runs the width of the head assembly and is integral with the inner core leg of each head in the assembly. The magnetic head assemblies disclosed in these two patents are disadvantageous because separate magnetic shields must be provided between individual magnetic heads. Moreover, where magnetic ferrite is integral to several magnetic heads, shunting of the magnetic field to adjacent heads increases the likelihood of signal degrading crosstalk.